18" × 6 TPI BUTT (pull type) Internal Thread Specifications
18-6 BUTT-2B · 18.0000-6 BUTT-2B
ASMESTD: ASME B1.9SOURCE: Table 3, Tables 1, 2, 5TYPE: Internal (nut/tapped hole)CLASS: 2BFLANKS 7° / 45°ROOT: roundTable 1 combination
Thread profile
18-6 BUTT-2B: solid = maximum material, dotted = minimum material. Flanks 7° (pressure) and 45° (clearance) from the radial line, 52° thread angle; drawn to scale.
Limits of size, class 2B
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter DnRoot of the female thread, min = D + 0.12542p; max for reference | 18.0000 | 18.0472ref. | 18.0209 | |
| Pitch diameter EMin = D − h | 17.9000 | 17.9125 | 17.9000 | 0.0125 |
| Minor diameter KnCrest of the female thread, min = D − 2h | 17.8000 | 17.8125 | 17.8000 | 0.0125 |
| Root radius rRound root, female (Fig. 1a) | 0.011902 | 0.005950 |
Dimensions in inches. Values are those of the standard (ASME B1.9); calculated cells follow the standard’s formulas. Where the standard prints a value that differs from its formula, the printed value is shown with a note.
Mating male thread, limits of size, class 2A
| Dimension | Basic | Max | Min | Tolerance |
|---|---|---|---|---|
| Major diameter dCrest of the male thread, max = D − G | 18.0000 | 17.9917 | 17.9792 | 0.0125 |
| Pitch diameter EMax = D − h − G | 17.9000 | 17.8917 | 17.8792 | 0.0125 |
| Minor diameter KsRoot of the male thread; min is a reference value | 17.8000 | 17.7708 | 17.7445ref. | 0.0263ref. |
| Allowance GSpace below basic size; equals the Class 3 PD tolerance (Sec. 7) | 0.0083 | |||
| Root radius rRound root, male (Fig. 1a) | 0.011902 | 0.005950 | ||
| Thread engagement heh − G/2 at max, less the PD tolerance at min | 0.095850 | 0.083350 |
Dimensions in inches. Values are those of the standard (ASME B1.9); calculated cells follow the standard’s formulas. Where the standard prints a value that differs from its formula, the printed value is shown with a note.
Lead, flank angle and length of engagement
- Lead + flank variation limit Σ
- 0.01250 inPitch diameter equivalent of lead and flank errors together (Class 2: the PD tolerance; Class 3: half)
- Lead variation alone ±δl
- 0.00702 inAllowable lead error if there is no flank error
- 45° flank angle variation alone ±δα
- 3.947 °Half-angle error of the clearance flank
- 7° flank angle variation alone ±δα
- 8.333 °Half-angle error of the pressure flank
Gaging Sections 10, 11 · Tables 6, 7, 8, 11
Male thread 18-6 BUTT-2A
- Gage pitch tolerance (W)
- 0.00030 in
- Gage 7° flank angle tolerance
- 5 min
- Gage 45° flank angle tolerance
- 5 min
- Gage major / minor tolerance
- 0.0013 in
- Gage pitch diameter tolerance
- 0.00060 in
- PD equivalent of pitch and flank tolerance
- 0.0009 in
- GO pitch diameter limit
- 17.8917 in
- NOT GO pitch diameter limit
- 17.8792 in
- NOT GO truncated crest diameter
- 17.8209 in
- Setting plug truncated major diameter
- 17.9584 in
- Best-size wire
- 0.09025 · C = 0.13647 in, C
- Maximum wire
- 0.10239 · C = 0.17476 in, C
Female thread 18-6 BUTT-2B
- Gage pitch tolerance (X)
- 0.00040 in
- Gage flank angle tolerance
- 5 min
- Gage major / minor tolerance
- 0.0013 in
- Gage pitch diameter tolerance
- 0.00120 in
- PD equivalent of pitch and flank tolerance
- 0.0011 in
- GO pitch diameter limit
- 17.9000 in
- NOT GO pitch diameter limit
- 17.9125 in
- NOT GO truncated crest diameter
- 17.9708 in
- Plain gage tolerance
- 0.00070 in
- Root relief width GO
- 0.027833 in
- Root relief width NOT GO
- 0.041667 in
Notes
- Class 2: no taper/roundness requirement (para. 6.6.1).
Mates
18-6 BUTT-2B takes a thread of the same standard at the same size and pitch. The standard mating external thread is class 2A. Check the fit with the standard pair →
Working out the mating options…
Different pitch or a different thread family never mate; the fit check runs over both tolerance zones.
Related thread sizes
Same diameter other pitch, and neighbouring sizes
All values for 18-6 BUTT-2Bevery column of the workbook row
| Designation | 18-6 BUTT-2B |
|---|---|
| Decimal designation | 18.0000-6 BUTT-2B |
| Threads per inch | 6 |
| Thread form | BUTT |
| Series (Table 1) | BUTT |
| Series name | Pull type, rounded root (default) |
| External / internal | Internal |
| Class | 2B |
| Nominal size (in.) | 18 |
| Pitch P (in.) | 0.16666667 |
| Basic major dia D (in.) | 18.0000 |
| Size category | Table 1 combination |
| Source table | Table 3, Tables 1, 2, 5 |
| Printed page | 4, 5, 6, 10 |
| Major dia max (in.) | 18.0472 |
| Major dia min (in.) | 18.0209 |
| Major dia status | Min = D + 0.12542P (basic); max is reference only = max PD + 0.80803P (para. 6.3, Sec. 4); no tolerance specified |
| Allowance G (in.; internal: mating external value, reference) | 0.0083 |
| Tolerance range (Tables 3-5) | Over 16 thru 24 |
| Range over (in.) | 16.0 |
| Range thru (in.) | 24.0 |
| Range mean dia for formula (in.) | 20.000 |
| Length of engagement Le = 10P (in.) | 1.6667 |
| Basic pitch dia E = D - h (in.) | 17.9000 |
| Pitch dia max (in.) | 17.9125 |
| Pitch dia min (in.) | 17.9000 |
| PD tolerance (in.) | 0.0125 |
| Basic minor dia K = D - 2h (in.) | 17.8000 |
| Minor dia max (in.) | 17.8125 |
| Minor dia min (in.) | 17.8000 |
| Minor dia tolerance (in.) | 0.0125 |
| Minor dia status | Toleranced: min = D - 2h (basic), max = min + PD tolerance (para. 6.2) |
| Root radius max (in.) | 0.011902 |
| Root radius min (in.) | 0.005950 |
| Root truncation s max (in.) | 0.013767 |
| Root truncation s min (in.) | 0.006883 |
| Engagement height he max (in.) | 0.095850 |
| Engagement height he min (in.) | 0.083350 |
| Lead + flank PD-equivalent limit (in.) | 0.01250 |
| Lead variation alone ± (in.) | 0.00702 |
| 45° flank variation alone ± (deg) | 3.947 |
| 7° flank variation alone ± (deg) | 8.333 |
| Lead angle at basic PD (deg) | 0.1698 |
| Lead angle (deg min) | 0° 10′ |
| Tensile stress area As (sq in.) | not given in the standard |
| Thread angle (deg) | 52 |
| Pressure (load) flank angle (deg) | 7 |
| Clearance flank angle (deg) | 45 |
| Flank orientation | Pull type (external thread pulls): 45° clearance flank leads, 7° load flank follows (Sec. 9) |
| Sharp V height H (in.) | 0.148440 |
| Basic thread engagement height h (in.) | 0.100000 |
| Thread height hs = hn (in.) | 0.110452 |
| Crest truncation f (in.) | 0.024220 |
| Crest width F (in.) | 0.027193 |
| Sweep cut: start diameter (in.) | 17.800000 |
| Sweep cut: tip diameter (in.) | 18.020900 |
| Sweep cut: depth (in.) | 0.110452 |
| Sweep cut: profile width at start diameter (in.) | 0.139473 |
| Sweep cut: tip width (root flat S max or radius r max) (in.) | 0.011902 |
| Constant c = 0.80803P (in.) | 0.134672 |
| PD tolerance component 0.00854√P (in.) | 0.003486 |
| X gage: pitch tolerance (in.) | 0.00040 |
| X gage: flank angle tolerance (min) | 5 |
| X gage: major/minor tolerance (in.) | 0.0013 |
| X gage: PD tolerance (in.) | 0.00120 |
| X gage: PD equivalent of pitch/flank tol. (in.) | 0.0011 |
| Z plain gage tolerance (in.) | 0.00070 |
| GO gage PD limit (in.) | 17.9000 |
| NOT GO gage PD limit (in.) | 17.9125 |
| NOT GO crest/minor truncated dia (in.) | 17.9708 |
| Root relief width GO (0.167P) (in.) | 0.027833 |
| Root relief width NOT GO (0.25P) (in.) | 0.041667 |
| Check against formulas | OK |
| Notes | Class 2: no taper/roundness requirement (para. 6.6.1). |
Related tools
- Thread standardsEvery ISO and ASME thread series and size, with limits and drawings.
- Thread Spec CalculatorDiameters, tolerances and geometry for ISO metric and unified threads.
- Thread Fit CheckPick a bolt and a nut and see the clearance or interference.
- Twist Drill SizesASME B94.11M drills: sizes, lengths, shanks and tolerances.
- Thread Designation GuideHow to read M10×1.5, 1/4-20 UNC-2A, NPT and more.
- Thread Notations & TermsSymbols and terms of a thread profile, explained.
ASME B1.9: Buttress Inch Screw Threads. Source: workbook data (2026-10-10). Confirm against your licensed copy of the standard before use.